feat: responsive pause/stop, non-blocking update with progress bar, delete saved sessions (1.5.0)

- carve: check cancellation inside chunks and per hit; reassembly stage is cancellable
- status exposes `stopping`; UI shows "Pausing…" immediately
- Tauri update commands run off the UI thread; download percentage reported
- delete autosaved sessions manually (one/all) and by retention setting
- chore(release): 1.5.0

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

apps/gui/src-tauri/Cargo.lock

@@ -1342,7 +1342,7 @@ dependencies = [
 
 [[package]]
 name = "guara-core"
-version = "1.4.0"
+version = "1.5.0"
 dependencies = [
  "aes",
  "argon2",
@@ -1373,7 +1373,7 @@ dependencies = [
 
 [[package]]
 name = "guara-gui"
-version = "1.4.0"
+version = "1.5.0"
 dependencies = [
  "guara-core",
  "libc",